Methods and compositions for reducing wear in internal combustion engines lubricated with a low phosphorous content borate-containing lubricating oil

ABSTRACT

Disclosed are methods and lubricant compositions for reducing wear in internal combustion engines lubricated with a low phosphorous content lubricating oil. The lubricant compositions of this invention comprise a synergistic combination of a dispersed, hydrated, alkali metal borate and at least one phosphorous-containing compound wherein the total phosphorous employed in the composition is no more than about 0.08 weight percent based on the total weight of the composition.

FIELD OF THE INVENTION

[0001] This invention is directed, in part, to methods and lubricantcompositions for reducing wear in internal combustion engines lubricatedwith a low phosphorous content lubricating oil. The lubricantcompositions of this invention comprise a synergistic combination of ananti-wear effective amount of a dispersed, hydrated alkali metal borateand at least one oil-soluble, phosphorous-containing, anti-wear compoundwherein the total phosphorous employed in the composition is no morethan about 0.08 weight percent based on the total weight of thecomposition.

[0002] References

[0003] The following references are cited in this application assuperscript numbers:

[0004]¹Buckley, III, Long Chain Aliphatic Hydrocarbyl Amine AdditivesHaving an Oxyalkylene Hydroxy Connecting Group, U.S. Pat. No. 4,975,096,issued Dec. 4, 1990

[0005]²Buckley, Methods and Compositions for Preventing thePrecipitation of Zinc Dialkyldithiophosphates Which Contain HighPercentages of a Lower Alkyl Group, U.S. Pat. No. 4,495,075, issued Jan.22, 1985

[0006]³Beck, et al., Impact of Oil-Derived Catalyst Poisons on FTPPerformance of LEV Catalyst Systems, SAE Technical Paper 972842 (1997)

[0007]⁴Johnson, et al., Effects of Oil-Derived Contaminants on Emissionsfrom TWC-Equipped Vehicles, SAE 200-01-1881 (2000)

[0008]⁵Baumgart, et al, Lubricant Additive Formulation, U.S. Pat. No.5,962,377, issued Oct. 5, 1999

[0009]⁶Adams, Synergistic Combination of Hydrated Potassium Borate,Anti-wear Agents, and Organic Sulfide Antioxidants, U.S. Pat. No.4,089,790, issued May 16, 1978

[0010]⁷Adams, Synergistic Combination of Hydrated Potassium Borate,Anti-wear Agents, and Organic Sulfide Antioxidants, U.S. Pat. No.4,163,729, issued Aug. 7, 1979

[0011]⁸Stoffa, et al., Borated Overbased Sulfonates for Improved GearPerformance in Functional Fluids, U.S. Pat. No. 5,635,459, issued Jun.3, 1997

[0012]⁹Clark, Automotive Friction Reducing Composition, U.S. Pat. No.4,534,873, issued Aug. 13, 1985

[0013] All of the above references are herein incorporated by referencein their entirety to the same extent as if each individual reference wasspecifically and individually indicated to be incorporated by referencein its entirety.

[0014] State of the Art

[0015] Emissions arising from automotive exhaust has been a problem forseveral decades and approaches for addressing this problem have includedthe use of unleaded fuel (to deal, in part, with lead emissions arisingfrom leaded fuels), oxygenated fuel (to reduce hydrocarbon emissions),the use of catalytic converters (also to reduce hydrocarbon emissions),etc.

[0016] Catalytic converters are now universally employed with gasolinepowered vehicles and the efficiency of these converters is directlyrelated to the ability of the catalyst to effect conversion of unburntor partially burnt hydrocarbons generated during combustion to carbondioxide and water. One problem arising with the use of such convertersis poisoning of the catalyst resulting in reduce catalyst efficiency.Since catalytic converters are intended for extended use, catalystpoisoning results in higher levels of atmospheric discharges ofpollutants from internal combustion engines over prolonged periods oftime.

[0017] In order to minimize such poisoning, the industry has setstandards for both fuel and lubricant contents. For example, standardsfor fuels have included the use of unleaded gasoline in order to avoidlead poisoning of the catalyst¹ as well as lead discharge into theenvironment.

[0018] As to the lubricants, one additive family currently beingaddressed by industry standards is the phosphorous-containing additivesused in lubricant compositions employed to lubricate internal combustionengines. Specifically, phosphorous-containing additives reach thecatalytic converter as a result of, for example, exhaust gasrecirculation and/or oil blow-by processes as well as other methodsknown in the art. See, for example, Beck, et al. and Johnson, etal.^(3,4) In any event, phosphorous is known to accumulate in thecatalytic converter and at active metal sites; thus reducing catalystefficiency and effectively over time, poisoning the catalyst. As aresult of the above, a new focus is to lower phosphorous in thelubricating oils. For example, the draft GF-4 specifications forlubricant compositions have proposed significantly lower phosphorouscontents than heretofore employed.

[0019] A problem arises when the level of phosphorous is reduced in alubricant composition containing an oil-soluble, phosphorous-containing,anti-wear compound in that there is a significant reduction in anti-wearperformance arising from this diminution in phosphorous content. Onewell known class of anti-wear additives are metal alkylphosphates,especially zinc dialkyl dithiophosphates, which are generally employedin lubricating oils at phosphorous levels above 0.1 weight percent whenused for wear control. At lower levels, it is not found to be aneffective anti-wear additive. For instance, as exemplified herein,lowering the level of phosphorous due to the presence of the zincdithiophosphate additive in a lubricant composition by one-half from0.095 weight percent to 0.048 weight percent phosphorous results inabout a seven-fold increase in engine wear.

[0020] This invention is directed to the discovery that lubricantcompositions comprising a combination of a complex of a dispersed,hydrated, alkali metal borate and low levels of one or more oil-soluble,phosphorous-containing, anti-wear compounds synergistically reduce wearlevels when used to lubricate gasoline engines.

[0021] With regard to the above, lubricant compositions comprising bothmetal dialkyl dithiophosphates and borated esters of sulfonic andcarboxylic acids are disclosed in, for example, U.S. Pat. No.5,962,377.⁵

[0022] Additionally, functional fluids useful as gear lubricants havepreviously employed combinations of phosphorus compounds such as zincdihydrocarbyl dithiophosphates and hydrated, alkali metalborates.^(6,7,8) Such compositions can employ up to 5 weight percent ofthe phosphorus compound^(6,7) or, in the case of Stoffa, et al.⁸, up to4 weight percent of the phosphorus compound.

[0023] Lubricant compositions containing a combination of three extremepressure, anti-wear agents comprising a dispersed, hydrated potassiumborate, an antimony dithiophosphate and a liquid chlorinated paraffinare disclosed by Clark.⁹ Such compositions can comprise up to 1.4 volumepercent of the antimony dithiophosphate in the finished lubricantcomposition.

SUMMARY OF THE INVENTION

[0024] As noted above, this invention is directed, in part, to lubricantcompositions comprising a combination of a dispersed, hydrated, alkalimetal borate and at least one oil-soluble, phosphorous-containinganti-wear compound wherein the total phosphorous employed in thecomposition is no more than about 0.08 weight percent based on the totalweight of the composition. This combination of additives synergisticallyreduces wear levels when used in lubricant compositions to lubricateinternal combustion engines.

[0025] Accordingly, in one of its composition aspects, this invention isdirected to a lubricating oil composition comprising a major amount ofan oil of lubricating viscosity,

[0026] at least one oil-soluble, phosphorous-containing, anti-wearcompound wherein the weight percent of total phosphorous in thecomposition is no more than about 0.08 weight percent based on the totalweight of the composition; and

[0027] an anti-wear effective amount of a dispersed, hydrated, alkalimetal borate.

[0028] In a preferred embodiment, the total phosphorous in thecomposition is no more than 0.06 and even more preferably no more thanabout 0.05 weight percent based on the total weight of the composition.

[0029] Preferably, the oil-soluble, phosphorous-containing, anti-wearcompound is selected from the group consisting of metaldithiophosphates, phosphorous esters (including phosphates,phosphonates, phosphinates, phosphine oxides, phosphites, phosphonites,phosphinites, phosphines and the like), amine phosphates and aminephosphinates, sulfur-containing phosphorous esters including phosphoromonothionate and phosphoro dithionates, phosphoramides, phosphonamidesand the like. More preferably, the phosphorous-containing compound is ametal dithiophosphate and, even more preferably, a zinc dithiophosphate.

[0030] In another preferred embodiment, the dispersed hydrated alkalimetal borate is present in an amount of from about 0.2 to about 5 weightpercent of the total weight of the lubricant composition and, even morepreferably, from about 0.5 to 2 weight percent.

[0031] Preferably, the dispersed hydrated alkali metal borate is adispersed hydrated potassium borate.

[0032] In one of its method aspects, this invention is directed to amethod for controlling wear during operation of an internal combustionengine, which method comprises operating the engine with a lubricantcomposition comprising a major amount of an oil of lubricatingviscosity, at least one oil-soluble, phosphorous-containing, anti-wearcompound wherein the weight percent of total phosphorous in thecomposition is no more than about 0.08 weight percent based on the totalweight of the composition, and an anti-wear effective amount of adispersed, hydrated alkali metal borate.

DETAILED DESCRIPTION OF THE INVENTION

[0033] This invention is directed, in part, to novel lubricantcompositions comprising a combination of a dispersed, hydrated alkalimetal borate and at least one oil-soluble, anti-wear,phosphorous-containing compound wherein the total phosphorous employedin the composition is no more than about 0.08 weight percent based onthe total weight of the composition.

[0034] Each of these components in the claimed composition will bedescribed in detail herein. However, prior to such a description, thefollowing terms will first be defined.

[0035] The term “an oil-soluble, phosphorous-containing, anti-wearcompound” refers to additives in lubricant compositions that containphosphorous and which exhibit an anti-wear benefit, either alone or whenused in combination with other additives, during operation of aninternal combustion engine that is lubricated with such a lubricantcomposition. The phosphorous in such additives is typically integral tothe additive.

[0036] The term “total phosphorous” refers to the total amount ofphosphorous in the lubricant composition regardless of whether suchphosphorous is present as part of an oil-soluble,phosphorous-containing, anti-wear compound or in the form of acontaminant in the lubricant composition such as residual phosphorousremaining due to the presence of P₂S₅ used to prepare metaldihydrocarbyl dithiophosphates. In either event, the amount ofphosphorous permitted in the lubricant composition is independent ofsource. Preferably, however, the phosphorous is part of a lubricantadditive.

The Hydrated Alkali Metal Borate

[0037] Hydrated alkali metal borates are well known in the art.Representative patents disclosing suitable borates and methods ofmanufacture include: U.S. Pat. Nos. 3,313,727; 3,819,521; 3,853,772;3,912,643; 3,997,454; and 4,089,790 all of which are incorporated hereinby reference in their entirety.

[0038] The hydrated alkali metal borates suitable for use in the presentinvention can be represented by the following general formula:

M₂O.xB₂O₃.yH₂O

[0039] wherein M is an alkali metal, preferably sodium or potassium; xis a number from 2.5 to 4.5 (both whole and fractional); and y is anumber from 1.0 to 4.8. More preferred are the hydrated potassiumborates, particularly the hydrated potassium triborates. The hydratedborate particles will generally have a mean particle size of less than 1micron.

[0040] In the alkali metal borates employed in this invention, the ratioof boron to alkali metal will preferably range from about 2.5:1 to about4.5:1.

[0041] Oil dispersions of hydrated alkali metal borates are generallyprepared by forming, in deionized water, a solution of alkali metalhydroxide and boric acid, optionally in the presence of a small amountof the corresponding alkali metal carbonate. The solution is then addedto a lubricant composition comprising an oil of lubricating viscosity, adispersant and any optional additives to be included therein (e.g., adetergent, or other optional additives) to form an emulsion that is thendehydrated.

[0042] Because of their retention of hydroxyl groups on the boratecomplex, these complexes are referred to as “hydrated alkali metalborates” and compositions containing oil/water emulsions of thesehydrated alkali metal borates are referred to as “oil dispersions ofhydrated alkali metal borates”.

[0043] Preferred oil dispersions of alkali metal borates will have aboron to alkali metal ratio of about 2.5:1 to about 4.5:1. In anotherpreferred embodiment, the hydrated alkali metal borate particlesgenerally will have a mean particle size of less than 1 micron. In thisregard, it has been found that the hydrated alkali metal boratesemployed in this invention preferably will have a particle size where90% or greater of the particles are less than 0.6 microns.

[0044] In the oil dispersion of hydrated alkali metal borate, thehydrated alkali metal borate will generally comprise about 10 to 75weight percent, preferably 25 to 50 weight percent, more preferablyabout 30 to 40 weight percent of the total weight of the oil dispersionof the hydrated borate. (Unless otherwise stated, all percentages are inweight percent.) This composition or concentrate is employed, often inthe form of an additive package, to form the finished lubricantcomposition. Sufficient amounts of the concentrate are added so that thefinished lubricant composition preferably comprises from about 0.2 toabout 5 weight percent of the total weight of the lubricant compositionand, even more preferably, from about 0.5 to 2 weight percent.

[0045] The lubricant compositions of this invention can further employsurfactants, detergents, other dispersants and other conditions asdescribed below and known to those skilled in the art.

[0046] The oil dispersions of hydrated alkali metal borates employed inthis invention generally comprise a dispersant, an oil of lubricatingviscosity, and optionally a detergent.

The Phosphorous-Containing Compound

[0047] Preferably, the oil-soluble, phosphorous-containing, anti-wearcompound employed in the compositions and methods of this invention isselected from the group consisting of metal dithiophosphates,phosphorous esters (including phosphates, phosphonates, phosphinates,phosphine oxides, phosphites, phosphonites, phosphinites, phosphines andthe like), amine phosphates and amine phosphinates, sulfur-containingphosphorous esters including phosphoro monothionate and phosphorodithionates, phosphoramides, phosphonamides and the like; all of whichare well known in the art. More preferably, the phosphorous-containingcompound is a metal dithiophosphate and, even more preferably, a zincdithiophosphate. Most preferably, the phosphorous containing compound isa zinc dialkyl dithiophosphate wherein the alkyl groups areindependently selected from C3 to C13, branched or straight chain carbongroups including mixtures thereof. Even more preferable, the phosphorouscontaining compound is zinc(II) bis(0,0′-di-(2-butyl/4-emthyl-2-pentyl)dithiophosphate.

[0048] The metal dithiophosphates are characterized by formula I:

[0049] wherein each R is independently a hydrocarbyl group containingfrom 3 to about 13 carbon atoms, M is a metal, and n is an integer equalto the valence of M.

[0050] The hydrocarbyl groups, R, in the dithiophosphate (or asdescribed elsewhere in this application) can be a C₃ to C₁₃ alkyl, C₃ toC₁₃ cycloalkyl, C₇ to C₁₃ aralkyl or C₇ to C₁₃ alkaryl groups, or asubstantially hydrocarbon group of similar structure. By “substantiallyhydrocarbon” is meant hydrocarbons that contain substituent groups suchas ether, ester, nitro, or halogen which do not materially affect thehydrocarbon character of the group.

[0051] Illustrative alkyl groups include isopropyl, isobutyl, n-butyl,sec-butyl, the various amyl groups, n-hexyl, methylisobutyl carbinyl,heptyl, 2-ethylhexyl, dilsobutyl, isooctyl, nonyl, behenyl, decyl,dodecyl, tridecyl, etc. Illustrative lower alkylphenyl groups includebutylphenyl, amylphenyl, heptylphenyl, etc. Cycloalkyl groups likewiseare useful and these include chiefly cyclohexyl and the loweralkyl-cyclohexyl radicals. Many substituted hydrocarbon groups may alsobe used, e.g., chlorophentyl, dichlorophenyl, and dichlorodecyl.

[0052] In another embodiment, at least one R group is an isopropyl orsecondary butyl group. In yet another embodiment, both R groups aresecondary alkyl groups.

[0053] The phosphorodithioic acids from which the metal salts useful inthis invention are prepared are well known. Examples of dihydrocarbylphosphorodithioic acids and metal salts, and processes for preparingsuch acids and salts are found in, for example, U.S. Pat. Nos.4,263,150; 4,289,635; 4,308,154; and 4,417,990. These patents are herebyincorporated by reference for such disclosures.

[0054] The phosphorodithioic acids are typically prepared by thereaction of phosphorous pentasulfide with an alcohol or phenol ormixtures of alcohols and/or phenols. The reaction involves four moles ofthe alcohol or phenol per mole of phosphorous pentasulfide, and may becarried out within the temperature range from about 50° C. to about 200°C. Thus, the preparation of O,O-di-n-hexyl phosphorodithioic acidinvolves the reaction of phosphorous pentasulfide with four moles ofn-hexyl alcohol at about 100° C. for about two hours. Hydrogen sulfideis liberated and the residue is the defined acid. The preparation of themetal salt of this acid may be effected by reaction with metal oxide.Simply mixing and heating these two reactants is sufficient to cause thereaction to take place and the resulting product is sufficiently purefor the purposes of this invention.

[0055] The metal dihydrocarbyl dithiophosphates that are useful in thisinvention include those salts containing Group I metals, Group IImetals, zinc, aluminum, lead, tin, molybdenum, manganese, cobalt, andnickel or mixtures thereof. The Group II metals, zinc, aluminum, tin,iron, cobalt, lead, molybdenum, manganese, nickel and copper are amongthe preferred metals. Zinc and copper either alone or in combination areespecially useful metals. Especially preferred is zinc. In oneembodiment, the lubricant compositions of the invention contain examplesof metal compounds which may be reacted with the acid include lithiumoxide, lithium hydroxide, sodium hydroxide, sodium carbonate, potassiumhydroxide, potassium carbonate, silver oxide, magnesium oxide, magnesiumhydroxide, calcium oxide, zinc hydroxide, zinc oxide, strontiumhydroxide, cadmium oxide, cadmium hydroxide, barium oxide, aluminumoxide, iron carbonate, copper hydroxide, lead hydroxide, tin burylate,cobalt hydroxide, nickel hydroxide, nickel carbonate, etc.

[0056] In some instances, the incorporation of certain ingredients suchas small amounts of the metal acetate or acetic acid (glacial) inconjunction with the metal reactant will facilitate the reaction andresult in an improved product. For example, the use of up to about 5% ofzinc acetate in combination with the required amount of zinc oxidefacilitates the formation of a zinc phosphorodithioate.

[0057] In one preferred embodiment, the alkyl groups, R, are derivedfrom secondary alcohols such as isopropyl alcohol, secondary butylalcohol, 2-pentanol, 4-methyl-2-pentanol, 2-hexanol, 3-hexanol, etc.Preferably R is derived from a mixure of secondary alcohols such as2-butanol and 4-methyl-2-pentanol. Particulary preferred R is derivedfrom the above mixture containing from about 65-75 weight percent2-butanol with the remainder 4-methyl-2-pentanol.

[0058] Especially useful metal phosphorodithioates can be prepared fromphosphorodithioic acids that, in turn, are prepared by the reaction ofphosphorous pentasulfide with mixtures of alcohols. In addition, the useof such mixtures enables the utilization of cheaper alcohols which inthemselves may not yield oil-soluble phosphorodithioic acids.

[0059] Useful mixtures of metal salts of dihydrocarbyl dithiophosphoricacid are obtained by reacting phosphorous pentasulfide with a mixture of(a) isopropyl or secondary butyl alcohol, and (b) an alcohol containingat least 5 carbon atoms wherein at least 10 mole percent, preferably 20or 25 mole percent, of the alcohol in the mixture is isopropyl alcohol,secondary butyl alcohol or a mixture thereof.

[0060] Thus, a mixture of isopropyl and hexyl alcohols can be used toproduce a very effective, oil-soluble metal phosphorodithioate. For thesame reason, mixtures of phosphorodithoic acids can be reacted with themetal compounds to form less expensive, oil-soluble salts.

[0061] The mixtures of alcohols may be mixtures of different primaryalcohols, mixtures of different secondary alcohols or mixtures ofprimary and secondary alcohols. Examples of useful mixtures include:n-butanol and n-octanol; n-pentanol and 2-ethyl-1-hexanol; isobutanoland n-hexanol; isobutanol and isoamyl alcohol; isopropanol and4-methyl-2-pentanol; isopropanol and sec-butyl alcohol; isopropanol andisooctyl alcohol; sec-butyl alcohol and 4-methyl-2-pentaol, etc.Particularly useful alcohol mixtures are mixtures of secondary alcoholscontaining at least about 20 mole percent and preferably at least 40mole percent of isopropyl alcohol. In a preferred embodiment, at least75 mole percent of sec-butyl alcohol is used and preferably combinedwith 4-methyl-2-pentanol, and most preferably further combined with azinc metal.

[0062] Particularly preferred metal dihydrocarbyl phosphorodithioatesinclude the zinc dithiophosphates. Patents describing the synthesis ofsuch zinc dithiophosphates include U.S. Pat. Nos. 2,680,123; 3,000,822;3,151,075; 3,385,791; 4,377,527; 4,495,075 and 4,778,906. Each of thesepatents is incorporated herein by reference in their entirety.

[0063] The following examples illustrate the preparation of metalphosphorodithioates and resulting metal dialkyldithiophosphates preparedfrom mixtures of alcohols.

EXAMPLE B1

[0064] A phosphorodithioic acid is prepared by reacting a mixture ofalcohols comprising 6 moles of 4-methyl-2-pentanol and 4 moles ofisopropyl alcohol with phosphorous pentasulfide. The phosphorodithioicacid then is reacted with an oil slurry of zinc oxide. The amount ofzinc oxide in the slurry is about 1.08 times and theoretical amountrequired to completely neutralize the phosphorodithioic acid. The oilsolution of the zinc phosphorodithioate obtained in this manner (10%oil) contains 9.5% phosphorous, 20.0% sulfur and 10.5% zinc.

EXAMPLE B2

[0065] A phosphorodithioioc acid is prepared by reacting finely powderedphosphorous pentasulfide with an alcohol mixture containing 11.53 moles(692 parts by weight) of isopropyl alcohol and 7.69 moles (1000 parts byweight) of isooctanol. The phosphorodithioic acid obtained in thismanner has an acid number of about 178-186 and contains 10.0%phosphorous and 21.0% sulfur. This phosphorodithioic acid is thenreacted with an oil slurry of zinc oxide. The quantity of zinc oxideincluded in the oil slurry is 1.10 times the theoretical equivalent ofthe acid number of the phosphorodithioic acid. The oil solution of thezinc salt prepared in this manner contains 12% oil, 8.6% phosphorous,18.5% sulfur and 9.5% zinc.

EXAMPLE B3

[0066] A phosphorodithioic acid is prepared by reacting a mixture of1560 parts (12 moles) of isooctyl alcohol and 180 parts (3 moles) ofisopropyl alcohol with 756 parts (3.4 moles) of phosphorouspentasulfide. The reaction is conducted by heating the alcohol mixtureto about 55° C. and thereafter adding the phosphorous pentasulfide overa period of 1.5 hours while maintaining the reaction temperature atabout 60-75° C. After all of the phosphorous pentasulfide is added, themixture is heated and stirred for an additional hour at 70-75° C., andthereafter filtered through a filter aid.

[0067] Zinc oxide (282 parts, 6.87 moles) is charged to a reactor with278 parts of mineral oil. The above-prepared phosphorodithioic acid(2305 parts, 6.28 moles) is charged to the zinc oxide slurry over aperiod of 30 minutes with an exotherm to 60° C. The mixture then isheated to 80° C. and maintained at this temperature for 3 hours. Afterstripping to 100° C. and 6 millimeters of mercury, the mixture isfiltered twice through a filter aid, and the filtrate is the desired oilsolution of the zinc salt containing 10% oil, 7.97% zinc (theory 7.40);7.21% phosphorous (theory 7.06); and 15.64% sulfur (theory 14.57).

EXAMPLE B4

[0068] Isopropyl alcohol (396 parts, 6.6 moles) and 1287 parts (9.9moles) of isooctyl alcohol are charged to a reactor and heated withstirring to 59° C. Phosphorous pentasulfide (833 parts, 3.75 moles) isthen added under a nitrogen sweep. The addition of the phosphorouspentasulfide is completed in about 2 hours at a reaction temperaturebetween 59-63° C. The mixture then is stirred at 45-63° C. for about1.45 hours and filtered. The filtrate is the desired phosphorodithioicacid.

[0069] A reactor is charged with 312 parts (7.7 equivalents) of zincoxide and 580 parts of mineral oil. While stirring at room temperature,the above-prepared phosphorodithioic acid (2287 parts, 6.97 equivalents)is added over a period of about 1.26 hours with an exotherm to 54° C.The mixture is heated to 78° C. and maintained at 75-85° C. for 3 hours.The reaction mixture is vacuum stripped to 100° C. at 19 millimeters ofmercury. The residue is filtered through a filter aid, and the filtrateis an oil solution (19.2% oil) of the desired zinc salt containing 7.86%zinc, 7.76% phosphorous and 14.8% sulfur.

EXAMPLE B5

[0070] The general procedure of Example B4 is repeated except that themole ratio of isopropyl alcohol to isooctyl alcohol is 1:1. The productobtained in this manner is an oil solution (10% oil) of the zincphosphorodithioate containing 8.96% zinc, 8.49% phosphorous and 18.05%sulfur.

EXAMPLE B6

[0071] A phosphorodithioic acid is prepared in accordance with thegeneral procedure of Example B4 utilizing an alcohol mixture containing520 parts (4 moles) of isooctyl alcohol and 360 parts (6 moles) ofisopropyl alcohol with 504 parts (2.27 moles) of phosphorouspentasulfide. The zinc salt is prepared by reacting an oil slurry of116.3 parts of mineral oil and 141.5 parts (3.44 moles of zinc oxidewith 950.8 parts (3.20 moles) of the above-prepared phosphorodithioicacid. The product prepared in this manner is an oil solution (10%mineral oil) of the desired zinc salt, and the oil solution containing9.36% zinc, 8.81% phosphorous and 18.65% sulfur.

EXAMPLE B7

[0072] A mixture of 520 parts (4 moles) of isooctyl alcohol and 559.8parts (9.33 moles) of isopropyl alcohol is prepared and heated to 60° C.at which time 672.5 parts (3.03 moles) of phosphorous pentasulfide areadded in portions while 15 stirring. The reaction then is maintained at60-65° C. for about one hour and filtered. The filtrate is the desiredphosphorodithioic acid.

[0073] An oil slurry of 188.6 parts (4 moles) of zinc oxide and 144.2parts of mineral oil is prepared, and 1145 parts of the above-preparedphosphorodithioic acid are added in portions while maintaining themixture at about 70° C. After all of the acid is charged, the mixture isheated at 80° C. for 3 hours. The reaction mixture then is stripped ofwater to 110° C. The residue is filtered through a filter aid, and thefiltrate is an oil solution (10% mineral oil) of the desired productcontaining 9.99% zinc, 19.55% sulfur and 9.33% phosphorous.

EXAMPLE B8

[0074] A phosphorodithioic acid is prepared by the general procedure ofExample B4 utilizing 260 parts (2 moles) of isooctyl alcohol, 480 parts(8 moles) of isopropyl alcohol, and 504 parts (2.27 moles) ofphosphorous pentasulfide. The phosphorodithioic acid (1094 parts, 3.84moles) is added to an oil slurry containing 181 parts (4.41 moles) ofzinc oxide and 135 parts of mineral oil over a period of 30 minutes. Themixture is heated to 80° C. and maintained at this temperature for 3hours. After stripping to 100° C. and 19 millimeters of mercury, themixture is filtered twice through a filter aid, and the filtrate is anoil solution (10% mineral oil) of the zinc salt containing 10.06% zinc,9.04% phosphorous, and 19.2% sulfur.

EXAMPLE B9

[0075] Isopropyl alcohol (410 parts, 6.8 moles) and 590 parts (4.5moles) 2-ethylhexyl alcohol are charged to a reactor and heated to 50°C. Phosphorous pentasulfide (541 parts, 2.4 moles) is added under anitrogen sweep. The addition is complete in 1.5 hours at a reactiontemperature of from 50-65° C. The contents are stirred for 2 hours andfiltered at 55° C. to give the desired phosphorodithioic acid.

[0076] A reactor is charged with 145 parts (3.57 equivalents) of zincoxide and 116 parts oil. Stirring is begun and added is 1000 parts (3.24equivalents) of the above obtained phosphorodithioc acid over a 1 hourperiod beginning at room temperature. The addition causes an exotherm to52° C. The contents are heated to 80° C. and maintained at thistemperature for 2 hours. The contents are then vacuum stripped to 100°C. at 22 millimeters mercury. Added is 60 parts oil and the contents arefiltered to give the desired product containing 12% oil, 9.5% zinc,18.5% sulfur and 8.6% phosphorous.

EXAMPLE B-10

[0077] A mixture of 2-butanol (237 parts, 77 mole) and4-methyl-2-pentanol (98 parts, 23 mole) was charged to a reactor with222 parts phosphorous pentasulfide at a temperature of about 75° C. andagitated for a period of about 2 hours. The reaction mixture was cooledand filtered to give the desired phosphorodithioic acid having aneutralization number of 193 (mgs. KOH/gram), a viscosity of 35.7 SSU at100 degrees Fahrenheit, a specific gravity of 1.04 (60/60) and contained24.0% sulfur and 11.9% phosphorous.

[0078] To the above mixture was added 87 parts by weight of zinc oxide,after which the whole was heated with agitation at about 54° C. for 4hours until a pH of 6.7 was reached. After the water of neutralizationhad been removed, the oil solution contained 7.6% zinc, 15.0% sulfur and7.2% phosphorous.

[0079] Another class of oil-soluble, phosphorous-containing, anti-wearcompounds is the class of phosphoramides and phosphonamides thatincludes thiophosphoramides and thiophosphonamides such as thosedisclosed in U.S. Pat. Nos. 3,909,430 and 3,968,157, the disclosures ofwhich are hereby incorporated by reference. These compounds may beprepared by forming a phosphorous compound having at least one P—N bond.They can be prepared, for example, by reacting phosphorous oxychloridewith a hydrocarbyl diol in the presence of a monoamine or by reactingphosphorous oxychloride with a difunctional secondary amine and amono-functional amine. Thiophosphoro amides can be prepared by reactingan unsaturated hydrocarbon compound containing from 2 to 450 or morecarbon atoms, such as polyethylene, polyisobutylene, polypropylene,ethylene, 1-hexene, 1,3-hexadiene, isobutylene, 4-methyl-1-pentene, andthe like, with phosphorous pentasulfide and a nitrogen-containingcompound as defined above, particularly an alkylamine, alkyldiamine,alkylpolyamine, or an alkyleneamine, such as ethylene diamine,diethylenetriamine, triethylenetetramine, tetraethylenepentamine, andthe like.

[0080] Still further phosphorous-containing compounds are oil-solublephosphates, phosphonates, phosphinates, or phosphine oxides representedby the formula II:

[0081] where R¹⁰, R²⁰ and R³⁰ are independently hydrogen or hydrocarbylgroups, X is oxygen or sulfur and a, b and c are independently 0 or 1.

[0082] The phosphorous-containing compounds can be an oil-solublephosphite, phosphonite, phosphinite or phosphine compound which can berepresented by the formula III:

[0083] where R¹⁰, R²⁰, R³⁰, a, b and c are as defined above.

[0084] The total number of carbon atoms in R^(10, R) ²⁰ and R³⁰ in eachof the above Formulae II and III must be sufficient to render thecompound soluble in the lubricating oil used in formulating theinventive compositions. Generally, the total number of carbon atoms inR¹⁰, R²⁰, and R³⁰ is at least about 8, and in one embodiment at leastabout 12, and in one embodiment at least about 16. There is no limit tothe total number of carbon atoms in R¹⁰, R²⁰ and R³⁰ that is required,but a practical upper limit is about 400 or about 500 carbon atoms. Inone embodiment, R¹⁰, R²⁰ and R³⁰ in each of the above formulae areindependently hydrocarbyl groups of 1 to about 100 carbon atoms, or 1 toabout 50 carbon atoms, or 1 to about 30 carbon atoms, with the provisothat the total number of carbons is at least about 8. Each R¹⁰, R²⁰ andR³⁰ can be the same as the other, although they may be different.Examples of useful R¹⁰, R²⁰ and R³⁰ groups include isopropyl, n-butyl,isobutyl, amyl, 4-methyl-2-pentyl, isooctyl, decyl, dodecyl, tetradecyl,2-pentenyl, dodecenyl, phenyl, naphthyl, alkylphenyl, alkylnaphthyl,phenylalkyl, naphthylalkyl, alkylphenylalkyl, alkylnaphthylalkyl, andthe like.

[0085] The phosphorous compounds represented by Formulae II and III canbe prepared by reacting a phosphorous acid or anhydride with an alcoholor mixture of alcohols corresponding to R¹⁰, R²⁰ and R³⁰ in Formulae IIand III. The phosphorous acid or anhydride is generally an inorganicphosphorous reagent such as phosphorous pentoxide, phosphorous trioxide,phosphorous tetraoxide, phosphorous acid, phosphorous halide, or lowerphosphorous esters, and the like. Lower phosphorous acid esters containfrom 1 to about 7 carbon atoms in each ester group. The phosphorous acidester may be a mono, di- or triphosphoric acid ester.

[0086] For a further discussion of the compounds of formulae II and IIIsee, for example, U.S. Pat. No. 5,712,230 that is incorporated herein byreference in its entirety.

[0087] Still another class of phosphorous containing compounds is theclass of oil-soluble, sulfur-containing phosphorous esters of formulaIV:

[0088] wherein R¹¹, R²¹, R³¹ and R⁴¹ are independently hydrocarbylgroups, X¹ and X² are independently O or S, and n is zero to 3. In oneembodiment X¹ and X² are each S, and n is 1. R¹¹, R²¹, R³¹ and R⁴¹ areindependently hydrocarbyl groups that are preferably free fromacetylenic unsaturation and usually also free from ethylenicunsaturation. In one embodiment R¹¹, R²¹, R³¹ and R⁴¹ independently havefrom about 1 to about 50 carbon atoms, and in one embodiment from about1 to about 30 carbon atoms, and in one embodiment from about 1 to about18 carbon atoms, and in one embodiment from about 1 to about 8 carbonatoms. Each of R¹¹, R²¹, R³¹ and R⁴¹ can be the same as the other,although they may be different and mixtures may be used. Examples ofR¹¹, R²¹, R³¹ and R⁴¹ groups include isopropyl, butyl, n-butyl,isobutyl, amyl, 4-methyl-2-pentyl, octyl, isooctyl, decyl, dodecyl,tetradecyl, 2-pentenyl, dodecenyl, phenyl, naphthyl, alkylphenyl,alkylnaphthyl, phenylalkyl, naphthylalkyl, alkylphenylalkyl,alkylnaphthylalkyl, and mixtures thereof.

[0089] Procedures for preparing the compounds of formula IV are wellknown in the art and are described, for example, in U.S. Pat. No.5,712,230 that is incorporated herein by reference in its entirety.

[0090] Still another class of oil-soluble, phosphorous-containing,anti-wear additives includes the amine phosphates and thiophosphatesthat are known in the art and disclosed, for example, in U.S. Pat. Nos.3,859,218; 5,585,029; and 6,040,279, all of which are incorporatedherein by reference in their entirety.

[0091] The amine phosphate for use in the compositions and methodsherein includes commercially available monobasic hydrocarbyl amine saltsof mixed mono- and di-acid phosphates and the amine salts of di-acidphosphate. The mono- and di-acid phosphates preferably have thestructural formulae VA and VB:

[0092] where each R is independently the same or different and arepreferably C₁ to C₁₂ linear or branched chain alkyl; each of R¹ and R²are independently hydrogen or C₁ to C₁₂ linear or branched chain alkyl;R³ is C₄ to C₁₂ linear or branched chain alkyl, or aryl-R⁴ or R⁴-arylwhere R⁴ is hydrogen or C₁ to C₁₂ linear or branched alkyl, and aryl isC₆.

[0093] The molar ratio of monoacid to diacid phosphate in the commercialamine phosphates used in this invention ranges from 3:1 to 1:3.

[0094] The mixed mono-/diacid phosphate and just the diacid phosphatecan be used with the latter being the preferred. One embodiment of anacid aliphatic aromatic amine-phosphate is Vanlube RTM 692, soldcommercially by the R. T. Vanderbilt Company, Inc.

The Oil of Lubricating Viscosity

[0095] The oil of lubricating viscosity used in the compositions andmethods of this invention may be mineral oils or synthetic oils ofviscosity suitable for use in the crankcase of an internal combustionengine. The base oils may be derived from synthetic or natural sources.Mineral oils for use as the base oil in this invention includeparaffinic, naphthenic and other oils that are ordinarily used inlubricating oil compositions. Synthetic oils include both hydrocarbonsynthetic oils and synthetic esters. Useful synthetic hydrocarbon oilsinclude liquid polymers of alpha olefins having the proper viscosity.Especially useful are the hydrogenated liquid oligomers of C₆ to C₁₂alpha olefins such as 1-decene trimer. Likewise, alkyl benzenes ofproper viscosity, such as didodecyl benzene, can be used. Usefulsynthetic esters include the esters of monocarboxylic acids andpolycarboxylic acids, as well as monohydroxy alkanols and polyols.Typical examples are didodecyl adipate, pentaerythritol tetracaproate,di-2-ethylhexyl adipate, dilaurylsebacate, and the like. Complex estersprepared from mixtures of mono and dicarboxylic acids and mono anddihydroxy alkanols can also be used. Blends of mineral oils withsynthetic oils are also useful.

Formulations

[0096] The compositions of this invention comprise the following:

[0097] an oil of lubricating viscosity;

[0098] at least one oil-soluble, phosphorous-containing, anti-wearcompound wherein the total phosphorous employed in the composition is nomore than about 0.08 weight percent based on the total weight of thecomposition (preferably no more than 0.06 weight percent);

[0099] an anti-wear effective amount of a dispersed, hydrated alkalimetal borate, and

[0100] optional additives.

[0101] In a particularly preferred embodiment, one optional additiveemployed in the compositions of this invention is an overbaseddetergent.

[0102] Preferably, the amount of dispersed, hydrated alkali metal borateemployed in these compositions is from about 0.2 to about 5 weightpercent (preferably from about 0.5 to about 2 weight percent based onthe total weight) based on the total weight of the composition.

[0103] Preferably, the amount of oil of lubricating viscosity ranges upto about 99 weight percent of the composition based on the total weightof the composition.

[0104] These compositions are prepared merely by mixing the appropriateamounts of each of these components until a homogenous composition isobtained.

[0105] The following additive components are examples of some of thecomponents that can be optionally employed in the compositions of thisinvention. These examples of additives are provided to illustrate thepresent invention, but they are not intended to limit it:

[0106] (1) Metal detergents: sulfurized or unsulfurized alkyl or alkenylphenates, alkyl or alkenyl aromatic sulfonates, sulfurized orunsulfurized metal salts of multi-hydroxy alkyl or alkenyl aromaticcompounds, alkyl or alkenyl hydroxy aromatic sulfonates, sulfurized orunsulfurized alkyl or alkenyl naphthenates, metal salts of alkanoicacids, metal salts of an alkyl or alkenyl multiacid, and chemical andphysical mixtures thereof.

[0107] A preferred class of metal detergents are overbased detergents.Overbased detergents include overbased metallic detergents preferablyhaving a TBN of greater than about 50 and more preferably greater thanabout 200 and even more preferably greater than about 250. Preferredmetals in such metallic detergents include alkali and alkaline earthmetals such as lithium, sodium and potassium. Particularly preferredmetals include calcium and magnesium and especially calcium. Typicaloverbased detergents include overbased phenates, salicylates andsulfonates which typically have a TBN of up to about 550.

[0108] (2) Oxidation inhibitors

[0109] (a) Phenol type oxidation inhibitors: 4,4′-methylenebis(2,6-di-tertbutylphenol), 4,4′-bis(2,6-di-tert-butylphenol),4,4′-bis(2-methyl-6-tert-butylphenol), 2,2′-methylenebis(4-methyl-6-tert-butylphenol), 4,4′-butylenebis(3-methyl-6-tert-butylphenol), 4,4′-isopropylenebis(2,6-di-tert-butylphenol), 2,2′-methylenebis(4-methyl-6-nonylphenol), 2,2′-isobutylene bis(4,6-dimethylphenol),2,2′-methylene bis(4-methyl-6-cyclohexylphenol),2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol,2,4-dimethyl-6-tert-butylphenol,2,6-di-tert-.alpha.-dimethylamino-p-cresol,2,6-di-tert-4-(N.N′dimethylaminomethylphenol),4,4′-thiobis(2-methyl-6-tert-butylphenol),2,2′-thiobis(4-methyl-6-tert-butylphenol), andbis(3-methyl-4-hydroxy-5-tert-butylbenzyl)-sulfide.

[0110] (b) Diphenyl amine type oxidation inhibitor: alkylated diphenylamine, phenyl-.alpha.-naphthylamine, and alkylated.alpha.-naphthylamine.

[0111] (c) Other types: metal dithiocarbamate (e.g., zincdithiocarbamate), and methylenebis (dibutyidithiocarbamate).

[0112] (3) Rust inhibitors (Anti-rust agents)

[0113] (a) Nonionic polyoxyethylene surface active agents:polyoxyethylene lauryl ether, polyoxyethylene higher alcohol ether,polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether,polyoxyethylene octyl stearyl ether, polyoxyethylene oleyl ether,polyoxyethylene sorbitol monostearate, polyoxyethylene sorbitolmono-oleate, and polyethylene glycol monooleate.

[0114] (b) Other compounds: stearic acid and other fatty acids,dicarboxilic acids, metal soaps, fatty acid amine salts, metal salts ofheavy sulfonic acid, partial carboxylic acid ester of polyhydricalcohol, and phosphoric ester.

[0115] (4) Demulsifiers:

[0116] addition product of alkylphenol and ethylene oxide,poloxyethylene alkyl ether, and polyoxyethylene sorbitan ester.

[0117] (5) Extreme pressure agents (EP agents):

[0118] sulfurized oils, diphenyl sulfide, methyl trichlorostearate,fluoroalkyl-polysiloxane, and lead naphthenate.

[0119] (6) Friction modifiers:

[0120] fatty alcohol, fatty acid, amine, borated ester (such as boratedglycerol monooleate), and other esters.

[0121] (7) Multifunctional additives:

[0122] sulfurized oxymolybdenum dithiocarbamate, sulfurizedoxymolybdenum organo phosphoro dithioate, oxymolybdenum monoglyceride,oxymolybdenum diethylate amide, amine-molybdenum complex compound, andsulfur-containing molybdenum complex compound.

[0123] (8) Viscosity index improvers:

[0124] polymethacrylate type polymers, ethylene-propylene copolymers,styrene-isoprene copolymers, hydrated styrene-isoprene copolymers,polyisobutylene, and dispersant type viscosity index improvers.

[0125] (9) Pour point depressants:

[0126] polymethyl methacrylate.

[0127] (10) Foam Inhibitors:

[0128] alkyl methacrylate polymers and dimethyl silicone polymers.

[0129] Preferably, the compositions of this invention do not include anyliquid chlorinated paraffins.

EXAMPLES

[0130] The invention will be further illustrated by the followingexamples, which set forth particularly advantageous method embodiments.While the examples are provided to illustrate the present invention,they are not intended to limit it.

[0131] As used in these examples and elsewhere in the specification, thefollowing abbreviations have the following meanings. If not defined, theabbreviation will have its art recognized meaning. cSt = centiStokes mL= milliliters mm = millimeters MW = molecular weight ppm = parts permillion s = seconds TBN = total base number VI = viscosity index

[0132] In addition, all percents recited below are weight percents basedon the total weight of the composition described unless indicatedotherwise.

Comparative Example 1

[0133] The purpose of this comparative example is to measure the effecton wear in an internal combustion engine arising from lowering theamount of a known anti-wear agent (zinc dithiophosphate) byapproximately 50% in a lubricant composition employed to lubricate aninternal combustion engine.

[0134] Specifically, two fully formulated lubricating oil compositionswere prepared using the following additives: Succinimide dispersant(2300 MW) 2.9 weight percent Borated succinimide dispersant (1300 MW)1.8 weight percent High overbased calcium phenate detergent  55millimoles (250 TBN) Zinc dithiophosphate (sufficient to provide 0.0475or 0.095 weight percent phosphorous) antioxidant 1.0 weight percent VIimprover 4.5 weight percent antifoam   5 ppm pour point depressant 0.3weight percent

[0135] In each case, the balance of the composition comprised a basestock comprising a Group II base oil having a kinematic viscosity of 4.5cSt at 100° C. to provide for a 5W20 oil.

[0136] The composition comprising 0.0475 weight percent phosphorous aszinc dithiophosphate is referred to hereafter as “0.0475% P” and thecomposition comprising 0.095 weight percent phosphorous as zincdithiophosphate is referred to hereafter as “0.095% P”.

[0137] These comparative compositions described were tested for wearperformance in a Sequence IVA engine test. The Sequence IVA testevaluates a lubricant's performance in preventing camshaft lobe wear inan overhead camshaft engine. More specifically, the test measures theability of crankcase oil to control camshaft lobe wear forspark-ignition engines equipped with an overhead valve-train and slidingcan followers. This test is to simulate service for taxicab,light-delivery truck, or commuter vehicles.

[0138] The Sequence IVA test method is a 100-hour test involving 100hourly cycles; each cycle consists of two operating modes or stages.Unleaded “Haltermann KA24E Green” fuel is used. The text fixture is aKA24E Nissan 2.4-liter, water-cooled, fuel-injected engine, 4-cylinderin-line, overhead camshaft with two intake valves, and one exhaust valveper cyclinder.

[0139] At the end of the test, each of the 12 cam lobes is measure atseven locations using a profilometer, which measures maximum depth ofwear. Measurements of wear on all seven positions of each lobe areadded; then all 12 lobe measurements are averaged for the wear result.This result is the primary evaluation for the test. Secondary resultscan include cam lobe nose wear and engine oil parameters. At 100 hours,the used oil is evaluated for: kinematic viscosity; fuel dilution; andwear metals iron (Fe) and copper (Cu). Pass/fail criteria includeaverage cam wear of 120 mm maximum. This test is currently underconsideration as an ASTM standard and is currently performed bycommercial engine test laboratories in accordance with draft No. 6having a revision date of January 2002.

[0140] In this engine test, wear is measured in microns of metal removedfrom the cam lobe and is reported as ACW uncorrected. Higher values ofmetal removed correspond to poor wear properties of the oil. The resultsof this evaluation are set forth in the table below: Example Amount ofWear Comparative Example (0.0475% P) 332.3 microns Comparative Example(0.095% P)  45.6 microns

[0141] These results evidence that by lowering the amount of phosphorousin the composition (due to zinc dithiophosphate) by 50% results in anapproximate 7 fold increase in wear.

Example 1

[0142] The purpose of this example is to demonstrate that acceptablewear performance is achieved using less than 0.08 weight percentphosphorous in the lubricant composition when the composition comprisesa dispersed, hydrated, alkali metal borate.

[0143] Specifically, two fully formulated lubricating oil compositionswere prepared using the following additives: Succinimide dispersant(2300 MW) 2.8 weight percent Low overbased calcium sulfonate degergent5.5 millimoles High overbased calcium phenate detergent  55 millimolesZinc dithiophosphate (sufficient to provide 0.03 or 0.095 weight percentphosphorous) VI improver 9.4 weight percent

[0144] In each case, the balance of the composition comprised a basestock comprising a Group II base oil having a kinematic viscosity of10.4 cSt at 100° C. to provide for a SAE viscosity grade 5W30 oil.

[0145] Since these compositions did not include any dispersed, hydratedalkali metal borate, these compositions were labeled “ComparativeExample C” (0.03 weight percent phosphorus) and “Comparative Example D”(0.095 weight percent phosphorus).

[0146] Two further formulations, identical to Comparative Examples C andD above were prepared with the exception that these compositions furthercomprised 2 weight percent of a dispersed, hydrated potassium boratecomposition (OLOA 9750®—available from Chevron Oronite Company, LLC,Houston, Tex. USA). Both of these compositions are compositions of thisinvention which were labeled Examples 2A (0.03 weight percentphosphorus) and 2B (0.095 weight percent phosphorus).

[0147] The compositions described above were tested for wear performancein a Mini-Traction Machine (MTM) bench test. The MTM is manufactured byPCS Instruments and operates in the pin-on-disk configuration in which astationary pin (0.25 inches 8620 steel ball) is loaded against arotating disk (32100 steel). The conditions employ a load of 25 Newtons,a speed of 500 mm/s and a temperature of 150° C.

[0148] In this bench test, wear is measured in microns of metal removedbetween the pin and the disk. Higher values of metal removed correspondto poor wear of the oil. The results of this evaluation are set forth inthe table below: Example Amount of Wear Comparative Example C 22.7microns Comparative Example D  7.3 microns Example 2A  8.6 micronsExample 2B  7.4 microns

[0149] These results evidence that in the absence of the dispersed,hydrated, alkali metal borate, significant wear occurred at a phosphoruslevel of approximately 0.03 weight percent and that approximately 3times the amount of phosphorus was required to reduce wear to 7.3microns. These results further evidence that in the presence of 2 weightpercent of the dispersed, hydrated potassium borate composition,acceptable wear results were achieved (8.6 microns) using only 0.03weight percent phosphorus.

[0150] From the foregoing description, various modifications and changesin the above described invention will occur to those skilled in the art.All such modifications coming within the scope of the appended claimsare intended to be included therein.

What is claimed is:
 1. A lubricating oil composition comprising a majoramount of an oil of lubricating viscosity, at least one oil-soluble,phosphorous-containing, anti-wear compound wherein the weight percent oftotal phosphorous in the composition is no more than about 0.08 weightpercent based on the total weight of the composition; and an anti-weareffective amount of a dispersed, hydrated, alkali metal borate.
 2. Thelubricating oil composition of claim 1 wherein the total phosphorous inthe composition is no more than 0.05 weight percent based on the totalweight of the composition.
 3. The lubricating oil composition of claim 1wherein the oil-soluble, phosphorous-containing, anti-wear compound isselected from the group consisting of metal dithiophosphates,phosphorous esters, amine phosphates and amine phosphinates,sulfur-containing phosphorous esters, phosphoramides and phosphonamides.4. The lubricating oil composition of claim 3 wherein said phosphorousesters are selected from the group consisting of phosphates,phosphonates, phosphinates, phosphine oxides, phosphites, phosphonites,phosphinites, and phosphines.
 5. The lubricating oil composition ofclaim 3 wherein said sulfur-containing phosphorous esters are selectedfrom the group consisting of phosphoro monothionate and phosphorodithionates.
 6. The lubricating oil composition of claim 3 wherein theoil-soluble, phosphorous-containing, anti-wear compound is a metaldithiophosphate.
 7. The lubricating oil composition of claim 6 whereinthe metal dithiophosphate is a zinc dialkyldithiophosphate.
 8. Thelubricating oil composition of claim 1 wherein the dispersed, hydrated,alkali metal borate is selected from the group consisting of dispersed,hydrated, sodium borates and dispersed, hydrated, potassium borates. 9.The lubricating oil composition of claim 8 wherein said dispersed,hydrated, alkali metal borate is a dispersed, hydrated, sodium borate.10. The lubricating oil composition of claim 8 wherein said dispersed,hydrated, alkali metal borate is a dispersed, hydrated, potassiumborate.
 11. A method for controlling wear during operation of aninternal combustion engine, which method comprises operating the enginewith a lubricant composition comprising a major amount of an oil oflubricating viscosity, at least one oil-soluble, phosphorous-containing,anti-wear compound wherein the weight percent of total phosphorous inthe composition is no more than about 0.08 weight percent based on thetotal weight of the composition, and an anti-wear effective amount of adispersed, hydrated alkali metal borate.
 12. The method according toclaim 11 wherein the total phosphorous in the composition is no morethan 0.05 weight percent based on the total weight of the composition.13. The method according to claim 11 wherein the oil-soluble,phosphorous-containing, anti-wear compound is selected from the groupconsisting of metal dithiophosphates, phosphorous esters, aminephosphates and amine phosphinates, sulfur-containing phosphorous esters,phosphoramides and phosphonamides.
 14. The method according to claim 13wherein said phosphorous esters are selected from the group consistingof phosphates, phosphonates, phosphinates, phosphine oxides, phosphites,phosphonites, phosphinites, and phosphines.
 15. The method according toclaim 13 wherein said sulfur-containing phosphorous esters are selectedfrom the group consisting of phosphoro monothionate and phosphorodithionates.
 16. The method according to claim 15 wherein thephosphorous containing compound is a metal dithiophosphate.
 17. Themethod according to claim 16 wherein the metal dithiophosphate is a zincdialkyldithiophosphate.